Metabolic reprogramming in cancer cells has been recognized as one of the most significant hallmarks of cancer. Tumorigenesis is dependent on the reprogramming of cellular metabolism as both direct and indirect consequence of oncogenic mutations. The alterations in intracellular and extracellular metabolites, that can accompany cancer-associated metabolic reprogramming, have profound effects on gene expression, cellular differentiation and tumor microenvironment and support rapid growth, metastasis, drug resistance and survival (Cancer Cell 2008, 13, 472-482; Cold Spring Harb Perspect Biol 2012, 4, a006783). Among the several changes of tumor metabolic pathways, abnormal choline metabolism is emerging as one of the metabolic hallmarks associated with oncogenesis and tumour progression. Activated choline metabolism, which is characterized by an increase in total choline-containing compounds (tCho) and, in particular, in phosphocholine (PCho) level, has been identified in tumor cells both in in vitro and in vivo studies, and by magnetic resonance spectroscopy (MRS) in primary tumors samples (Cancer & Metabolism 2016, 4, 12-14; Biochimica et Biophysica Acta 2013, 1831, 1518-1532; NMR Biomed. 2012, 25, 632-642; Semin. Oncol. 2011, 38, 26-41; Lancet Oncol. 2007, 8, 889-97). Choline phospholipid metabolism consists of a complex network of biosynthetic and catabolic pathways controlled by several regulatory enzymes that may be potential targets for anticancer therapy (Prog. Lipid Res. 2016, 63, 28-40; Nat. Rev. Cancer, 2011, 11, 835-848). Among the enzymes involved, Choline Kinase (ChoK) is ubiquitously distributed in eukaryotes and catalyzes the first step of the Kennedy pathway for the de novo synthesis of phosphatidylcholine (PtdCho), which is the most abundant phospholipid in mammalian cellular membranes (IUBMB Life 2010, 62, 414-428; J. Lipid Res. 2008, 49, 1187-1194). In mammalian cells two separate genes encode for three isoforms: ChoKα1, ChoKα2 and ChoKβ. ChoKα1 and ChoKα2 are formed as the result of alternative splicing of the CHKA transcript. The enzyme is active as homo or hetero dimers (Prog. Lipid Res. 2004, 43, 266-281). In the first step of the Kennedy pathway, ChoK converts choline into phosphocholine (PCho), which then reacts with cytidine triphosphate (CTP) to form cytidine diphosphate-choline (CDP-choline). The PCho moiety is then transferred to diacylglycerol to produce PtdCho. Moreover PCho is considered a putative second messenger involved in proliferation and its level increase is correlated to activity of ChoKα in cells (J Cell. Bioch. 1995, 57, 141-149; J. Biol. Chem. 1997, 272, 3064-3072).
Different and not redundant roles for ChoKα and ChoKβ have been suggested. ChoKα knock-out mice result in embryonic lethality (J. Biol. Chem. 2008, 283, 1456-1462), while ChoKβ knock-out mice develop a rostrocaudal muscular dystrophy and bone deformity (J. Biol. Chem. 2006, 281, 4938-4948). In human, an inactivating mutation in CHKB gene has been identified in congenital muscular dystrophy (Am. J. Hum. Genet. 2011, 88, 845-851; Curr. Opin. Neurol. 2013, 26: 536-543). Moreover ChoKα, but not ChoKβ, has been associated with malignancy and its down modulation using specific siRNA is sufficient to affect PCho level, invasion and migration of cancer cells (FEBS Journal 2012, 279, 1915-1928; Adv. Enzyme Regul. 2011, 51, 183-194; PLoS ONE 2009, 4, e7819). According to these data, ChoKα inhibition could be sufficient to have an antitumor activity avoiding potential toxic effect linked to ChoKβ inhibition.
Several data reported in the literature support the role of ChoKα in tumors. Down modulation or overexpression of ChoKα induce a clear effect on PCho levels and, consequently, affect in vitro invasiveness, migration and growth in several cell lines (i.e. ovary, breast, prostate cancer cells) (Mol. Cancer Ther. 2016, 15, 1-11; JNCI J. Natl. Cancer Inst. 2016, 108, 371-384; Oncogene 2010, 29, 139-149; Current Cancer Drug Targets 2008, 8, 709-719; Cancer Res. 2005, 65, 11034-43). Depletion of ChoKα in cell lines stably transfected with ChoKα specific shRNA showed a reduced ability to grow in vivo (Cancer Res. 2009, 69, 3464-3471), as well as forced over-expression has been shown to cause an increased tumor formation and aggressiveness of the disease (NMR Biomed 2010, 23, 633-642; Oncogene 2009, 28, 2425-2435).
In tumor samples, high expression of ChoKα or high levels of choline metabolites are correlated to aggressiveness of tumors like ovary, breast, brain and lung (Front. Oncol. 2016, 6, 153; Carcinogenesis 2015, 36, 68-75; Mol. Cancer Ther. 2015, 14, 899-908; BJC 2015, 112, 1206-1214; Cancer Biol. Ther. 2014, 15, 593-601; Cancer Res. 2014, 74, 6867-77; BCR 2014, 16, R5; NMR Biomed. 2011, 24, 316-324; BBRC 2002, 296, 580-3). Metabolomic analysis of prostate samples in in vitro and in vivo models as well as in tumor samples revealed that AKT1 activation is associated with accumulation of aerobic glycolysis metabolites, whereas MYC overexpression is associated with a dysregulated lipid metabolism and induction of ChoKα (Cancer Res. 2014, 74, 7198-204). Recently it has been reported that also T-cell lymphoma is characterized by high levels of ChoKα and choline metabolites and that genetic ablation of ChoKα, using specific siRNA, induces inhibition of proliferation and apoptotis both in vitro and in vivo (Blood Cancer J. 2015, 5, 287-296). Choline metabolites (total choline, tCho) can be monitored in patients by Magnetic Resonance Spectroscopy (MRS) or by Positron Emission Tomography (PET) and it is under evaluation as potential biomarker in preclinical and clinical studies (Expert Rev. Mol. Diagn. 2015, 15, 735-747).
Choline metabolism is also involved in drug resistance. Over-expression of ChoKα increases invasiveness and drug resistance to 5-fluorouracil (5FU) in human breast cancer cells (NMR Biomed. 2010, 23, 633-642), as well as inhibition of ChoKα activity seems to be sinergistic with 5FU in colon cancer cell lines both in vitro and in vivo (PloS ONE 2013, 8, e64961-74).
ChoKα silencing in different epithelial ovarian cancer cells induces a reduction in the tumorigenic properties of these cells. This antitumor activity was correlated to a specific altered ROS homeostasis induced by a reduction in cysteine and glutathione (GSH) levels in ChoKα-depleted cells. This effect was observed in tumor cells, but not in non-tumorigenic cells, and it is mediated by a decrease of the trans-sulphuration pathway (BJC 2014, 110, 330-340). This outcome in ovarian cancer cells is also linked to increased drug sensitivity to cisplatin, doxorubicin and paclitaxel (Oncotarget 2015, 6, 11216-11230).
Choline Kinase has been identified as a potential target also in other diseases. In rheumatoid arthritis (RA) it has been demonstrated that inhibition of ChoKα suppresses cell migration and resistance to apoptosis of cultured fibroblast-like synoviocytes (FLS), involved in cartilage destruction in RA. Moreover inhibition of ChoKα abrogates joint inflammation and damage in either pretreatment or established disease protocols in K/B×N arthritis mouse model (Ann. Rheum. Dis. 2015, 74, 1399-1407).
ChoK is the first enzyme in the Kennedy pathway (CDP-choline pathway) for the biosynthesis of PtdCho also in malaria-causing Plasmodium parasites. Based on pharmacological and genetic data, the de novo biosynthesis of PtdCho appears to be essential for the intraerythrocytic growth and survival of the malaria parasite. This highlights the potential use of ChoK inhibitors, active on ChoK of Plasmodium parasites (e.g. Plasmodium falciparum), in the fight against malaria (Curr. Pharm. Des. 2012, 18, 3454-3466; Precision Medicine 2015; 2: e980-992).
Functional genomics studies identified ChoKα as a new target for Hepatitis C (HCV) or B (HBV), because it seems to be involved in entry as well as in replication of the virus inside the target cells (Scientific Reports 2015, 5, 8421-8429; PLOS Pathogens 2014, 10, e1004163-77).
ChoK inhibitors have already been reported in WO2014151761 (ARIAD PHARMACEUTICALS INC.), WO200568429 (Consejo Superior de Investigacions Cientificas, Universidad de Granada), WO200777203 (Consejo Superior de Investigacions Cientificas, Universidad de la Laguna), WO2015185780 (Universidad de Granada and Università degli Studi di Padova), WO2013043961 and WO2013043960 (both by Vertex).